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At least 181 records · Page 10
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Fourier-method beam analysis for coherent vertical cavity surface emitting laser arrays

Effective engineering and exploitation of coherently coupled vertical cavity surface emitting laser arrays will benefit from simple and fast characterization of the optical coupling and coherence. We propose a Fourier method of analyzing beam profiles as an alternative to the prior beam visibility analysis and show that the mode suppression ratio and phase between a pair of supermodes can be extracted. Our analysis enables fast quantitative determination of the array coherence and supermode characteristics.

Strzebonski, Pawel (ORCID:0000000156286296)↗
DOE OSTI2018

Application of Quad-Scan Measurement Techniques to Muon Beams in the Muon g-2 Experiment

Determination of the properties of a beam during transport is a vital process for most accelerator-related experiments; for example Fermilab's Muon g-2 experiment requires large numbers of muons to be stored in a storage ring of 7 meter radius, and the transmission fraction has been shown to depend strongly on the properties of the beam, specifically the Twiss parameters. The current equipment in the muon campus beamlines allows only measurement of beam profiles which limits how well propagation can be predicted, however by using the well-studied quad-scan technique it is possible to obtain all of the Twiss parameters at a point using these profiles. Experimental quad-scans of muon beams have not yet been reported, this paper introduces the quad-scan technique and then goes on to discuss the analysis of one such experiment and the results obtained, showing that such a technique is applicable in the muon g-2 experiment to obtain the Twiss parameters without requiring installation of new equipment.

43 PARTICLE ACCELERATORS↗
DOE OSTI2016

SU-F-T-459: ArcCHECK Machine QA : Highly Efficient Quality Assurance Tool for VMAT, SRS & SBRT Linear Accelerator Delivery

Purpose: Quality assurance (QA) of complex linear accelerators is critical and highly time consuming. ArcCHECK Machine QA tool is used to test geometric and delivery aspects of linear accelerator. In this study we evaluated the performance of this tool. Methods: Machine QA feature allows user to perform quality assurance tests using ArcCHECK phantom. Following tests were performed 1) Gantry Speed 2) Gantry Rotation 3) Gantry Angle 4)MLC/Collimator QA 5)Beam Profile Flatness & Symmetry. Data was collected on trueBEAM stX machine for 6 MV for a period of one year. The Gantry QA test allows to view errors in gantry angle, rotation & assess how accurately the gantry moves around the isocentre. The MLC/Collimator QA tool is used to analyze & locate the differences between leaf bank & jaw position of linac. The flatness & Symmetry test quantifies beam flatness & symmetry in IEC-y & x direction. The Gantry & Flatness/Symmetry test can be performed for static & dynamic delivery. Results: The Gantry speed was 3.9 deg/sec with speed maximum deviation around 0.3 deg/sec. The Gantry Isocentre for arc delivery was 0.9mm & static delivery was 0.4mm. The maximum percent positive & negative difference was found to be 1.9 % & – 0.25 % & maximum distance positive & negative diff was 0.4mm & – 0.3 mm for MLC/Collimator QA. The Flatness for Arc delivery was 1.8 % & Symmetry for Y was 0.8 % & X was 1.8 %. The Flatness for gantry 0°,270°,90° & 180° was 1.75,1.9,1.8 & 1.6% respectively & Symmetry for X & Y was 0.8,0.6% for 0°, 0.6,0.7% for 270°, 0.6,1% for 90° & 0.6,0.7% for 180°. Conclusion: ArcCHECK Machine QA is an useful tool for QA of Modern linear accelerators as it tests both geometric & delivery aspects. This is very important for VMAT, SRS & SBRT treatments.

43 PARTICLE ACCELERATORS↗
DOE OSTI2019

An Eigenvector-Based Method of Radio Array Calibration and Its Application to the Tianlai Cylinder Pathfinder

We propose an eigenvector-based formalism for the calibration of radio interferometer arrays. In the presence of a strong dominant point source, the complex gains of the array can be obtained by taking the first eigenvector of the visibility matrix. We use the stable principle component analysis method to help separate outliers and noise from the calibrator signal to improve the performance of the method. This method can be applied with poorly known beam model of the antenna, is insensitive to outliers or imperfections in the data, and has low computational complexity. It thus is particularly suitable for the initial calibration of the array, which can serve as the initial point for more accurate calibrations. We demonstrate this method by applying it to the cylinder pathfinder of the Tianlai experiment, which aims to measure the dark energy equation of state using the baryon acoustic oscillation features in the large-scale structure by making intensity mapping observation of the redshifted 21 cm emission of the neutral hydrogen (H i). The complex gain of the array elements and the beam profile in the east–west direction (short axis of the cylinder) are successfully obtained by applying this method to the transit data of bright radio sources.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

SU-F-T-481: Physics Evaluation of a Newly Released InCise™ Multileaf Collimator for CyberKnife M6™ System

Purpose: This work reports the results of the physics evaluation of a newly released InCise™2 Multileaf Collimator (MLC) installed in our institution. Methods: Beam property data was measured with unshielded diode and EBT2 films. The measurements included MLC leaf transmission, beam profiles, output factors and tissue-phantom ratios. MLC performance was evaluated for one month after commissioning. Weekly Garden Fence tests were performed for leaf / bank positioning in standard (A/P) and clinically relevant non-standard positions, before and after MLC driving exercises of 10+ minutes. Daily Picket Fence test and AQA test, End-to-End tests and dosimetric quality assurance were performed to evaluate the overall system performance. Results: All measurements including beam energy, flatness and symmetry, were within manufacture specifications. Leaf transmission was 0.4% <0.5% specification. The values of output factors ranged from 0.825 (7.6 mm × 7.5 mm) to 1.026 (115.0 mm × 100.1 mm). Average beam penumbra at 10 cm depth ranged from 2.7mm/2.7mm(7.6 mm × 7.5 mm) to 6.0 mm/6.2mm(84.6 mm × 84.7 mm). Slight penumbra difference (<10% from average penumbra for fields >20 mm) was observed in the direction perpendicular to leaf motion due to the tilting of the leaf housing. Mean leaf position offsets was −0.08±0.07mm and −0.13 ± 0.08 for X1 and X2 leaf banks in 13 Garden Fence tests. No significant difference on average leaf positioning offsets was observed between different leaf orientations and before/after MLC driving exercises. Six End-to-End tests showed 0.43±0.23mm overall targeting accuracy. Picket-Fence and AQA showed stable performance of MLC during the test period. Dosimetric point dose measurements for test cases agreed with calculation within 3%. All film measurements on relative dose had Gamma (2%, 2mm) passing rate of >95%. Conclusion: The Incise™2 MLC for CyberKnife M6™ was proven to be accurate and reliable, and it is currently in clinical use. Stanford was one of the physics evaluation sites for the newly released InCise 2 MLC for Accuray Inc.

07 ISOTOPE AND RADIATION SOURCES↗
DOE OSTI2018

Application of Geant4 Monte Carlo simulation in dose calculations for small radiosurgical fields

The Geant4 toolkit was used to develop a Monte Carlo (MC)-based engine for accurate dose calculations in small radiation field sizes. The Geant4 toolkit (version 10.1.p02) was used to simulate 6-MV photon beam of a Varian2100C linear accelerator that is being used for stereotactic radiosurgery (SRS) treatment with small radiation fields. Geometric models of 3 in-house designed radiosurgical divergent cones, with the diameters of their projections at the isocenter being 10, 20, and 30 mm, were simulated. The accuracy of the MC simulation technique was examined by reproducing several different simulated dosimetric parameters of the primary beams with the experimental data. The dose distributions are first checked for single beams for each cone, then standard multiple field (SMF) techniques are applied. A sample set of DICOM files from computed tomography (CT) scan imaging of a patient's head was converted to the Geant4 geometry format to implement MC-based engine for a clinical test. To validate the accuracy of the MC-based calculations for SMF arrangements, the isodose lines from MC simulation in water phantom were compared with the measured isodose lines using EBT3 Gafchromic film in Solid Water phantoms. Agreements between measured and simulated depth dose values and beam profiles for SRS cones were generally within 2%/2 mm. For output factors, the largest discrepancy was observed for 10 mm SRS cone, which was 1.7%. For SMF techniques, in SRS cones, the MC simulation and EBT3 Gafchromic film dosimetry were in acceptable agreement (5%/5 mm). Excellent agreement between the results of the MC-based and measured dose values for both single and SMF techniques in SRS cones indicates the ability of the Geant4 toolkit to be applied as the platform for treatment planning of advanced radiotherapy techniques.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2016

SU-F-T-74: Experimental Validation of Monaco Electron Monte Carlo Dose Calculation for Small Fields

Purpose: To verify experimentally the accuracy of Monaco (Elekta) electron Monte Carlo (eMC) algorithm to calculate small field size depth doses, monitor units and isodose distributions. Methods: Beam modeling of eMC algorithm was performed for electron energies of 6, 9, 12 15 and 18 Mev for a Elekta Infinity Linac and all available ( 6, 10, 14 20 and 25 cone) applicator sizes. Electron cutouts of incrementally smaller field sizes (20, 40, 60 and 80% blocked from open cone) were fabricated. Dose calculation was performed using a grid size smaller than one-tenth of the R{sub 80–20} electron distal falloff distance and number of particle histories was set at 500,000 per cm{sup 2}. Percent depth dose scans and beam profiles at dmax, d{sub 90} and d{sub 80} depths were measured for each cutout and energy with Wellhoffer (IBA) Blue Phantom{sup 2} scanning system and compared against eMC calculated doses. Results: The measured dose and output factors of incrementally reduced cutout sizes (to 3cm diameter) agreed with eMC calculated doses within ± 2.5%. The profile comparisons at dmax, d{sub 90} and d{sub 80} depths and percent depth doses at reduced field sizes agreed within 2.5% or 2mm. Conclusion: Our results indicate that the Monaco eMC algorithm can accurately predict depth doses, isodose distributions, and monitor units in homogeneous water phantom for field sizes as small as 3.0 cm diameter for energies in the 6 to 18 MeV range at 100 cm SSD. Consequently, the old rule of thumb to approximate limiting cutout size for an electron field determined by the lateral scatter equilibrium (E (MeV)/2.5 in centimeters of water) does not apply to Monaco eMC algorithm.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2016

SU-F-T-260: Using Portal Image Device for Pre-Treatment QA in Volumetric Modulated Arc Plans with Flattening Filter Free (FFF) Beams

Purpose: To implement and validate a method of using electronic portal image device (EPID) for pre-treatment quality assurance (QA) of volumetric modulated arc therapy (VMAT) plans using flattering filter free (FFF) beams for stereotactic body radiotherapy (SBRT). Methods: On Varian Edge with 6MV FFF beam, open field (from 2×2 cm to 20×20 cm) EPID images were acquired with 200 monitor unit (MU) at the image device to radiation source distance of 150cm. With 10×10 open field and calibration unit (CU) provided by vendor to EPID image pixel, a dose conversion factor was determined by dividing the center dose calculated from the treatment planning system (TPS) to the corresponding CU readout on the image. Water phantom measured beam profile and the output factors for various field sizes were further correlated to those of EPID images. The dose conversion factor and correction factors were then used for converting the portal images to the planner dose distributions of clinical fields. A total of 28 VMAT fields of 14 SBRT plans (8 lung, 2 prostate, 2 liver and 2 spine) were measured. With 10% low threshold cutoff, the delivered dose distributions were compared to the reference doses calculated in water phantom from the TPS. A gamma index analysis was performed for the comparison in percentage dose difference/distance-to-agreement specifications. Results: The EPID device has a linear response to the open fields with increasing MU. For the clinical fields, the gamma indices between the converted EPID dose distributions and the TPS calculated 2D dose distributions were 98.7%±1.1%, 94.0%±3.4% and 70.3%±7.7% for the criteria of 3%/3mm, 2%/2mm and 1%/1mm, respectively. Conclusion: Using a portal image device, a high resolution and high accuracy portal dosimerty was achieved for pre-treatment QA verification for SBRT VMAT plans with FFF beams.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2018

Enhanced high-order harmonic generation driven by a wavefront corrected high-energy laser

We developed and implemented an experimental setup for the generation of high-energy high-order harmonics in argon gas for nonlinear experiments in the extreme ultraviolet (XUV) spectral range. High-order harmonics were generated by loosely focusing a high-energy laser pulse centered around 800 nm into a gas cell filled with argon in a phase-matching condition. The wavefront distortions of the driving pulse were corrected by a deformable mirror, and the XUV conversion efficiency was significantly improved due to the excellent beam profile at focus. A high-damage-threshold beam splitter was used to eliminate high-energy driving pulses co-propagating with high-order harmonics. The setup has a potential to provide intense ultrashort XUV pulses reaching the intensity levels required for nonlinear experiments in the XUV spectral range.

74 ATOMIC AND MOLECULAR PHYSICS↗
NASA NTRS2006

Comparison of NASA's 30-cm Ion Thruster Capabilities with the Dawn Mission Requirements

The Dawn ion thrusters meet all of the performance and life requirements for the Dawn mission. FT001 has two magnets in sideways in the middle magnet ring, but this has only a minor impact on the thruster performance. Electron-backstreaming is the first wear-out failure mechanism for the Dawn ion thrusters - PFA Modeling Indicates: a) The mission cannot be completed with a single thruster; b) The probability for mission success based on accelerator grid wear is > 99% for the worst case thruster usage for nominal thruster beamlet profiles; and c) FT002 has the most peaked beam profile which impacts the thruster s throughput capability. PFA results indicate that this reduces the probability for mission success based on accelerator grid wear to 97% based on the worst case thruster usage. The wear-out probability is zero if all three thrusters are used during the mission.

ion thrusters↗
NASA NTRS2013

Status of Multi-Beam Long Trace- Profiler Development

A multi-beam LTP is under development at MSFC in collaboration with Lawrence Berkeley National laboratory and Brookhaven National Laboratory. The Multi-beam LTP has been fully assembled. First tests of the MBLTP has demonstrated the feasibility of the multibeam approach. The calibrations are under way. The MBLTP is intended to be used for metrology support of the deterministic polishing experiments.

Gubarev, Mikhail V.↗
DOE OSTI2024

Author Correction: Proton irradiation-decelerated intergranular corrosion of Ni-Cr alloys in molten salt

In the original version of this article, numbers for the beam current densities were incorrectly given as 1.5, 2.0, and 2.5 mA cm -2 in various locations, instead of the correct values 0.3, 0.4, and 0.5 mA cm -2 . This was owing to a measurement error coming from the indirect correspondence between the Faraday cup and the beam profile monitor (BPM) on the accelerator as the proton beam traveling along the beamline resulted in mismatching between calculated values and real beam currents, which were obtained by ex-situ calibration. The following changes have been made in the correct version. The eighth sentence of the Results, and the figure legend of Fig. 2j state '0.3, 0.4, 0.5 mA cm -2 ' in place of '1.5, 2.0, 2.5 mA cm -2 '. The figure legend of Fig. 1j–l states '0.5, 0.4, 0.3 mA cm -2 ' in place of '2.5, 2.0, 1.5 mA cm -2 '. Figure 1e states '0.5 mA cm -2 ' in place of '2.5 mA cm -2 ', Fig. 1h states '0.4 mA cm -2 ' in place of '2.0 mA cm -2 ', and Fig. 1k states ‘0.3 mA cm -2 ' in place of ‘1.5 mA cm -2 '. Figure 2c states '0.5 mA cm -2 ' in place of '2.5 mA cm -2 ', Fig. 2d states '0.4 mA cm -2 ' in place of '2.0 mA cm -2 ', and Fig. 2e states '0.3 mA cm -2 ' in place of '1.5 mA cm -2 '. Figure 2j and k states ‘0.3 mA cm -2 ', '0.4 mA cm -2 ', '0.5 mA cm -2 ' in place of '1.5 mA cm -2 ', '2.0 mA cm -2 ', and '2.5 mA cm -2 ', respectively. The figure legend of Fig. 3b states '0.4 mA cm -2 ' in place of '2.0 mA cm -2 '. The figure legend of Supplementary Fig. 1 states '0.5 mA cm -2 ' in place of '2.5 mA cm -2 '. This has been corrected in the PDF and HTML versions of the Article.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Design and Testing of Subsystems for Mo-99 Production

Argonne National Laboratory, in cooperation with Los Alamos National Laboratory, is developing technology with NorthStar Medical Technologies to produce 99 Mo from the γ,n reaction on a 100 Mo target in an electron accelerator. During production runs and thermal testing of the helium-cooled target, it became obvious that a production-scale beam-line configuration would need a collimator to protect the target from accidental beam misplacement or a beam-profile change. A prototype high-power collimator and beam stop were designed and fabricated. Testing indicated that they will be able to operate at full power in the production-scale accelerator.

43 PARTICLE ACCELERATORS↗
DOE OSTI2019

Beam Tests of the PIP-II Injector Test Radio Frequency Quadrupole

In modern high intensity ion-particle accelerators, a Radio Frequency Quadrupole (RFQ) is utilized to prepare a high-quality beam for injection to the main accelerating section. Since an RFQ governs the initial beam parameters, characterization of the beam coming out from the RFQ is foremost step toward commissioning of an accelerator facili-ty. It allows validating the RFQ design as well as attaining a better understanding of charged-particle beams. This pa-per describes the beam-performance of the Proton Improvement Plan-II Injector Test (PIP2IT) Continuous Wave (CW) four vane-type RFQ. It is designed to operate at a frequency of 162.5 MHz and accelerate a nominal H- beam of 5 mA from 30 keV to 2.1 MeV. The paper details beam tests performed to validate the RFQ design specifications for trans-mission, beam kinetic energy and, RMS emittances. The paper also presents beam profile measurements and implica-tion of the beam-jitters on the effective beam emittance at the RFQ exit.

43 PARTICLE ACCELERATORS↗
DOE OSTI2019

Photon diagnostics at the FLASH THz beamline

The THz beamline at FLASH, DESY, provides both tunable (1–300 THz) narrow-bandwidth (&sim;10%) and broad-bandwidth intense (up to 150 uJ) THz pulses delivered in 1 MHz bursts and naturally synchronized with free-electron laser X-ray pulses. Combination of these pulses, along with the auxiliary NIR and VIS ultrashort lasers, supports a plethora of dynamic investigations in physics, material science and biology. The unique features of the FLASH THz pulses and the accelerator source, however, bring along a set of challenges in the diagnostics of their key parameters: pulse energy, spectral, temporal and spatial profiles. Here, these challenges are discussed and the pulse diagnostic tools developed at FLASH are presented. In particular, a radiometric power measurement is presented that enables the derivation of the average pulse energy within a pulse burst across the spectral range, jitter-corrected electro-optical sampling for the full spectro-temporal pulse characterization, spatial beam profiling along the beam transport line and at the sample, and a lamellar grating based Fourier transform infrared spectrometer for the on-line assessment of the average THz pulse spectra. Corresponding measurement results provide a comprehensive insight into the THz beamline capabilities.

47 OTHER INSTRUMENTATION↗
DOE OSTI2022

Polished diamond X-ray lenses

High-quality bi-concave 2D focusing diamond X-ray lenses of apex-radius R = 100 µm produced via laser-ablation and improved via mechanical polishing are presented here. Both for polished and unpolished individual lenses and for stacks of ten lenses, the remaining figure errors determined using X-ray speckle tracking are shown and these results are compared with those of commercial R = 50 µm beryllium lenses that have similar focusing strength and physical aperture. For two stacks of ten diamond lenses (polished and unpolished) and a stack of eleven beryllium lenses, this paper presents measured 2D beam profiles out of focus and wire scans to obtain the beam size in the focal plane. These results are complemented with small-angle X-ray scattering (SAXS) measurements of a polished and an unpolished diamond lens. Again, this is compared with the SAXS of a beryllium lens. The polished X-ray lenses show similar figure errors to commercially available beryllium lenses. While the beam size in the focal plane is comparable to that of the beryllium lenses, the SAXS signal of the polished diamond lenses is considerably lower.

47 OTHER INSTRUMENTATION↗
DOE OSTI2018

Comparison of profile measurements and TRANSPORT beam envelope predictions along the 80-m LANSCE pRad beamline

Here in this paper we report a comparison between the simulation of beam phase-space and profile distributions with diagnostic measurements. TRANSPORT, a particle transport code, was used for the prediction of a 800MeV proton beam envelope from the end of the linac to the proton radiography (pRad) facility (a total length of 80 meters). The beam profile was measured at key positions along the beamline using wire scanners and gated CCD camera systems. These measurements were compared to their respective points along the simulated beamline. The predicted beam envelope and measured data correspond within expected errors.

47 OTHER INSTRUMENTATION↗
DOE OSTI2020

NuMI Beam Muon Monitor Data Analysis and Simulation for Improved Beam Monitoring

The NuMI muon monitors (MMs) are a very important diagnostic tool for monitoring the stability of the neutrino beam used by the NOvA experiment at Fermilab. The goal of our study is to maintain the quality of the MM signal and to establish the correlations between the neutrino and muon beam profile. This study could also inform the LBNF decision on the beam diagnostic tools. We report on the progress of beam scan data analysis (beam position, spot size, and magnetic horn current scan) and comparison with the simulation outcomes.

43 PARTICLE ACCELERATORS↗